The application for setting up enhanced uplink in TD-SCDMA (Time Division Synchronous Code Division Multiple Access) system was approved by 3GPP (3rd Generation Partnership Project) in March 2006. The enhanced uplink is generally called HSUPA (High Speed Uplink Packet Access), which aims for improving the efficiency of the uplink through advanced technique, thereby effectively supporting web browse, video, multimedia information and other IP-based services.
Although there is no complete technical report at present concerning the TD-SCDMA HSUPA technology of 3GPP, its basic technical framework has been developed, which can refer to the proposal and conference report about 3GPP conference held in Shanghai in May, as well as the technical framework related to the present invention in the following description.
A transmission channel E-DCH (Enhanced-uplink Dedicated transmission Channel) for carrying the enhanced uplink data is added in HSUPA, and the TTI (Transmission Time Interval) of the E-DCH is 5 ms.
The physical channels matching the E-DCH are:
E-AGCH (E-DCH absolute grant channel), which is a control channel used for Node B to transmit grant information; E-PUCH (E-DCH physical uplink channel, also called enhanced physical uplink channel), which is a traffic channel used for the UE (User Equipment) to carry E-DCH encoding combination and scheduling related information;
E-RUCCH (E-DCH Random access Uplink Control Channel, namely HSUPA random access uplink control channel), which is a physical control channel used to transmit the scheduling related information when UE has not been granted, and which uses random access physical channel resource;
E-HICH (E-DCH hybrid automatic repeat request indication channel), which is a physical layer control channel used for Node B to carry HARQ (Hybrid Automatic Repeat Request) indication information.
According to scheduling method, HSUPA service is divided into scheduling service and non-scheduling service, wherein the non-scheduling service has its resource assigned to UE by SRNC (Serving Radio Network Controller), and its assignment method is the same as that of the dedicated channel in the prior art; In the scheduling service, SRNC assigns the HSUPA resource pool to Node B which then assigns resource to single UE and sends absolute grant information including power grant information and physical channel grant information to the UE through the E-AGCH. The power grant information is used to assign the available system interference resource among the competitive UEs; and the physical channel grant information is used to assign the time slot and code resource used by E-PUCH among the competitive UEs. One piece of grant information in the E-AGCH can be used by one UE each time, and the granted available minimal duration is one E-DCH TTI, or the grant of variable time interval is also supported by using RDI (Resource Duration Indication), for example, RDI can indicate the UE to use certain granted resource in the next 8 TTIs. The UE intercepts one group of E-AGCHs which are configured for the UE by the higher layer of network, and the UE reads the grant information once it decodes the information successfully, and sends data through the granted E-PUCH after the timing nE-AGCH prescribed by the protocol. The Node B decodes the received data in the E-PUCH, if decoding the data successfully, it returns ACK in the E-HICH; otherwise it returns NACK, meanwhile the UE needs to re-transmit the data according to retransmission mechanism.
In the scheduling service, the UE should submit some information for assisting the scheduling of Node B, which includes information of the UE buffer, margin of power and information of path loss measurement in present cell and neighboring cell. If the UE has a granted E-PUCH, the scheduling information will be sent through E-PUCH; otherwise, the information will be sent through E-RUCCH. When the UE has uplink data to be sent, the scheduling information may be triggered to be sent. The grant information is not sent to the UE at each TTI, rather, whether or not/when to send the information is completely decided by the scheduling function entity of Node B according to the current network condition and the priorities of each competitive UE.
FIG. 1 shows the working process of HSUPA scheduling service, wherein RRC (Radio Resource Control) connection between the UE and the SRNC has been established prior to step 101, and the reason for connecting the UE is to initiate packet service. The specific steps in FIG. 1 are described as follows:
101: Through admission control process, the SRNC assumes that it can establish HSUPA for the UE and sends a message through NBAP (Node B Application Protocol) to Node B for starting radio link establishment process, the message including parameters related to the enhanced uplink access, such as the information about the transmission channel, E-DCH serving radio link number, and so on; If a radio link was established for the UE before, the enhanced uplink parameters are configured through radio link reconfiguration process.
102: Node B receives the configuration parameters and assigns E-AGCH and E-RNTI (E-DCH Radio Network Temporary Identification) in the enhanced uplink common resource pool of the cell for the UE, which are returned to the SRNC through the radio link setup response or radio link reconfiguration response of NBAP.
103: The SRNC sends radio bearer setup command to the UE through RRC protocol, the command includes the information of E-DCH configuration, E-PUCH, E-AGCH and E-HICH; if the process of radio bearer setup was performed before, the enhanced uplink access will be configured through radio bearer reconfiguration process.
104: The UE receives the configuration parameters and returns a response to the network side; and it is determined that the E-DCH transmission service is available according to the configuration parameters.
105: If the data amount in the logical channel buffer corresponding to the UE E-DCH is changed from 0 to non-0, the UE, with the scheduling information, initiates E-RUCCH random access process.
106: After the Node B detects the random access request sent by the UE, it adds the UE into the group of competitive UEs which use E-DCH resource, schedules the UE according to the resource condition of the cell, the QOS attributes of the enhanced uplink radio bearer of the UE as well as the scheduling information of the UE, and sends the grant information to the UE through E-AGCH after suitable resource has been assigned to the UE.
107: After the UE has received the E-AGCH, it sends data through the granted E-PUCH after the timing nE-AGCH prescribed by the protocol; if there are still data in the UE buffer to be sent, the scheduling information will also be sent.
108: Node B decodes the data on the E-PUCH and returns ACK/NACK information through the E-HICH.
109: If the last E-AGCH granted available time has been expired, the Node B continues to assign resource to the UE according to the scheduling strategy and sends the grant information through the E-AGCH.
110-111: same as steps 107 and 108.
112: If there are still data to be sent in the UE buffer but there is no grant information at present, the UE will apply resource through E-RUCCH.
There are two definite time sequence relationships: nE-AGCH, which is decided by the protocol, is the timing interval between E-AGCH and the next first E-PUCH time slot; nE-HICH, which is selected by Node B and configured for the UE through SRNC, is the timing interval between the last E-PUCH time slot in one E-DCH TTI and the corresponding E-HICH.
The problem in the existing technology is: in the scheduling service, if the UE still has data to be sent when one E-AGCH granted available time has been expired while Node B has no appropriate resource to be scheduled to the UE, that is, the UE has not received the next E-AGCH in time, whether will the UE immediately send the scheduling information through E-RUCCH or continue to intercept the E-AGCH? E-RUCCH is a random access physical channel; in TD-SCDMA, the random access should go through the uplink synchronization process which is performed by sending uplink synchronous code at UpPTS (Uplink Pilot Time Slot) and receiving the timing and power adjustment information from the corresponding FPACH (Fast Physical Access Channel), by referring to 3GPP TS25.224 protocol for details, it can be seen that the access process is relatively complicated. Moreover, E-RUCCH is a common channel and there is possibility of competition conflicts; the frequent initiation of E-RUCCH access not only wastes network resource but also makes the UE consume a lot of electricity; in addition, if Node B has no appropriate resource to be scheduled, even if the UE sends E-RUCCH immediately, it will not receive a response.
Moreover, due to the competitiveness of E-RUCCH, the reliability of E-RUCCH transmission mechanism should be considered to ensure that Node B could correctly receive the scheduling request from the UE.